Package org.eclipse.debug.core.model

Package Specification

This package defines classes and interfaces known as the "debug model"
which support an extensible set of debug architectures and languages. The debug
model is a set of interfaces representing common artifacts in debuggable programs.
The debug plug-in itself does not provide an implementation of a debug model.
It is intended that third parties providing an integrated set of development
tools for a specific language will also implement a debug model for that language,
using an underlying debug architecture of their choice. For example, Java development
tooling provides an implementation of a debug model based on the standard Java
Platform Debug Architecture (JPDA).

The Debug Model

A client implements a debug model by
providing an implementation of the interfaces defined in this package. (There is no explicit
extension point that represents a debug model). Each debug model provides one or more
launch configuration types capable of initiating a debug session.

The common elements defined by the debug model are:

Debug Target - A debug target represents a debuggable program - for example, a virtual
machine or a process.

Thread - A debug target may contain one or more threads.

Stack Frame - A suspended thread may contain one or more stack frames.

Variable - A stack frame may contain variables.

Value - Each variable has an associated value, and a value may contain more variables (to
represent complex data structures and objects).

Register Group - A stack frame may (optionally) be associated with one or more register
groups.

Register - A register group contains one or more registers.

Memory Blocks - A debug target may (optionally) support the retrieval of
arbitrary contiguous segments of memory.

Breakpoint - Breakpoints suspend the execution of a program.

Expression - An expression is a snippet of code that can be evaluated to
produce a value.

A debug model implementation is responsible for firing debug events. A debug event
corresponds to an event in a program being debugged - for example the creation or
termination of a thread.

Breakpoints

Breakpoints are used to suspend the execution of a program being debugged. There are
many kinds of breakpoints - line breakpoints, conditional line breakpoints, hit count
breakpoints, exception breakpoints, etc. The kinds of breakpoints supported by each debug
architecture, and the information required to create those breakpoints
is dictated by each debug architecture. The debug platform supports an extensible
set of breakpoint via the breakpoints extension point.

The debug platform provides a breakpoint manager that maintains the collection
of all registered breakpoints. Clients add and remove breakpoints via this manager.
Breakpoints are implemented by instances of IBreakpoint. Each breakpoint
object has an associated marker, which provides persistence and presentation
in editors. The debug platform defines a generic breakpoint and line breakpoint,
as well as their corresponding marker definitions. Breakpoint creation is a
client responsibility - that is, defining the attributes of a breakpoint and
the resource to associate a breakpoint marker with.

Breakpoints are persisted via their underlying marker. Breakpoint markers defined
with the persisted attribute as false will not be persisted. Breakpoints
are restored at workspace startup time by the breakpoint manager - that is,
breakpoint objects are created for all persisted markers which are a subtype
of the root breakpoint marker and are added to the breakpoint manager. To allow
for selective persistence of breakpoints (of the same kind), the IBreakpoint
interface and root breakpoint implementation defines a "persisted"
attribute. If this value is set to false, the breakpoint will not be persisted
across workspace invocations.

As breakpoint markers are modified (created, removed, and changed), resource
deltas are created by the platform. The breakpoint manager translates pertinent
resource deltas into breakpoint change notifications (breakpoint added/removed/changed
messages). Interested listeners may register with the breakpoint manager. The
breakpoint manager only fires change notifications for registered breakpoints.
This simplifies breakpoint processing for clients, as resource delta traversal
and analysis is not required. Debug targets that support breakpoints should
register for breakpoint change notifications.

New Features in the Debug Model, Eclipse 3.0

Launch Delegate Enhancements

Lanuch delegates can optionally implement the new interface ILaunchConfigurationDelegate2.
This allows launch delegates to provide a launch object to be used for a launch.
For example, when debugging on a server a delegate could create a new launch
object or may reuse an existing launch object if the server is already running
in debug mode. As well, the inteface provides a mechanism for performing a
scoped build prior to launching (i.e. scoped to the projects in the workspace
pertaining to the launch), and searching for errors in the workspace which
may prevent the launch from succeeding (for example, compilation errors).

Extensible Watch Expressions

The debug platform provides an implementation of watch expressions. Debug
models can contribute watch expression delegates if they support watch expressions.
When a stack frame is selected, the associated delegate is queried to provide
a value for a watch expression in that context. The debug platform provides
persistence, enabling, disabling, entering, and editing of watch expressions.

Automatic Array Partitioning

The debug plug-in supports automatic partitioning of indexed collections,
which partitions large arrays into sub-ranges in the variables view. This
is supported with the introduction of a new interface in the debug model representing
an indexed value - IIndexedValue. If a value implements this
interface, the variables view will automatically partition its elements as
required, into sub-ranges

Logical Structure Types

Often, it is convenient to navigate complex data structures in terms of a
logical structure, rather than an implementation structure. For example, no
matter how a list is implemented (i.e. linked list, collection of arrays,
etc.), it is often convenient to be able to view the list as an ordered collection.
To facilitate the display of logical structures in the variables view, an
extension point has been added (org.eclipse.debug.core.logicalStructureTypes)
allowing debug models to contribute logical structures of its values, where
applicable. Debug models may contribute delegates to translate raw implementation
values into logical values. The variables view will display the logical values,
when the option to display logical structures is turned on. More than one
logical structure can be provided for a single value - the user can choose
which structure to display.

Step Filters

To support step filters on all stepping functions (into, over, return), a
new interface has been added to the debug platform - IStepFilters
- which can be implemented by debug targets. This interface replaces IFilteredStep,
which is now deprecated. The debugger provides a global toggle that turns
step filters on/off for all stepping functions. Debug targets should implement
this new interface and honor the step filter enablement setting when stepping.

This change maintains binary compatibility with previous releases. However,
targets wishing to leverage the new function must implement the new interface.